Process for forming thermally stable negative images on surfaces utilizing polyglutarimide polymer in photoresist composition

ABSTRACT

This invention relates to negative photoresist systems containing thermally stable polyglutarimide polymers dissolved in suitable solvents. The negative resists are useful for producing high resolution images on surfaces by exposing the resist to a wide range of exposing radiation wavelengths and by subsequently developing the unexposed resist with an organic solvent or an aqueous base developer. The polyglutarimide polymers can be formulated so that they are partially soluble in an aqueous base, compatible with aqueous base soluble photosensitizers, and developable in aqueous base solutions, thereby eliminating the need for the use of any organic solvent.

This is a division of application Ser. No. 571,053 filed Jan. 5, 1984,U.S. Pat. No. 4,569,897.

FIELD OF THE INVENTION

This invention relates to negative photoresist systems, and moreparticularly to negative photoresist systems containing imidized acrylicpolymers which possess high thermal stability, etch resistance and imageresolution.

BACKGROUND OF THE INVENTION

Negative-acting photoresists, commonly referred to as negative resists,are useful in photolithographic and photomasking operations infabricating microelectronic devices, printed circuits, semiconductors,printing plates, dies and the like. Negative resists typically contain acoupler resin and a photosensitizer compound dissolved in an organicsolvent. The negative resist film is deposited from the solvent on thesurface of a suitable substrate as by spin casting, dipping, spraying orscreen printing. In microelectronic applications, the substrate istypically a silicon or modified silicon plate or wafer and, in printedcircuit applications, a metal-clad plastic. After the film is depositedand the solvent is removed as by evaporation by the application ofelevated temperatures ("softbake"), a portion of the film is exposed toa source of radiation, such as ultraviolet light, through a photomask.The photosensitizer in the resist is selected because of its ability toabsorb the exposing radiation and cause the coupler resin to becomeinsoluble in a solvent that will dissolve the unexposed portions of theresist film. The conversion of the exposed film is typically caused by acrosslinking reaction of the coupler resin with the activatedphotosensitizer compound. The unexposed portion of the film is thenremoved by the application of a solvent, known as a developer, to forman image on the surface. The imaged surface may then be treated, as byetching, ion implantation or other processes useful in the production ofa functional integrated circuit. Following this treatment, the remainingexposed resist film may be removed or stripped by a suitable solvent.

DESCRIPTION OF THE PRIOR ART

Many different types of coupler resins have been proposed for use innegative resist systems. Conventional polymeric coupler resins includecyclized polyisoprene (U.S. Pat. Nos. 2,852,379 and 2,940,853)chloromethylated polystyrene, N-allyl maleimides (U.S. Pat. Nos.3,832,187; 3,902,920 and 3,905,820), n-halocyclic imides (U.S. Pat. No.3,702,766) and mixtures of N-maleimides and triallyl cynaurateprepolymers (U.S. Pat. No. 4,072,524). Photosensitizers which have beenfound useful in negative resist systems include organic solvent solublecompounds such as Michler's ketone (4,4'-bis dimethylaminobenzophenone), 2,6-bis-p-azidobenzal-4-methyl cyclohexanone,2-tertbutyl-9,10 anthraquinone, 1,2-benzo-9,10-anthraquinone,2-keto-3-methyl-1,3-diazobenzoanthrone, p-nitrodiphenyl, and the like.The coupler resin and photosensitizer are dissolved in common organicsolvents such as lower alcohols, ketones, dimethylformamide,tetrahydrofuran, pyridine, benzene, toluene, mixtures thereof and thelike. In general, any number of organic, non-reacting solvents in whichthe coupler resin and photosensitizer are soluble and which can act asan effective vehicle for the deposition of a photoresist film on asurface can be employed.

While a number of these negative resists have been employed inmanufacturing semiconductor and integrated circuit devices, thelimitations of these systems have become increasingly more apparent.Because of the increasing miniaturization of circuitry, the need forimage resolution on the order of a few micrometers, preferably as low asone to two micrometers, is required. Most conventional negative resistsare not capable of achieving such high image resolutions because theorganic solvent developers utilized tend to swell the crosslinked resistthereby reducing image resolution. The organic solvents used indepositing and developing conventional negative resists also presentpotential health, environmental and flammability problems. Conventionalnegative resists also suffer from inadequate resistance to the hightemperatures encountered in semi-conductor processing.

Thermal stability of the resist is important in achieving high imageresolution when the resist is processed. If the processing temperatureexceeds the glass transition temperature of the crosslinked couplerresin, the exposed resist layer will begin to melt or flow. Flow of theresist layer leads to reduced image resolution. The resist must alsopossess good resistance to etching accomplished either by wet etching,utilizing buffered aqueous hydrofluoric acid solutions containinghydrogen fluoride and ammonia, or dry plasma or reactive ion etching.

It is therefore, an object of this invention to provide a negativeresist which solves the problems encountered by those skilled in the artof negative resists.

It is also an object of the invention to provide a negative resistsystem which is capable of depositing an adhesive, high quality, stablefilm on a substrate surface which provides high image resolution andetch resistance.

It is a further object of the invention to provide negative resistsystems that minimize and eliminate the need for organic solvents todeposit and develop negative resists.

SUMMARY OF THE INVENTION

Thermally stable, negative resist systems, containing imidized acrylicpolymers dissolved in suitable solvents, with and withoutnegative-acting photosensitizers, are provided. A critical aspect ofthis invention is the discovery that imidized acrylic polymer-basednegative resists can be formulated and developed with aqueous solventseliminating the need for organic solvents while maintaining high imageresolution, excellent adhesion, thermal stability and etch resistance.

DETAILED DESCRIPTION OF THE INVENTION

I have found that imidized acrylic polymers, referred to herein aspolyglutarimides, can be mixed with negative acting photosensitizers anddissolved in selected solvents to form a novel negative photoresistsystem useful for depositing an adherent, thermally stable, high qualityfilm on a substrate surface, and that such a film is capable ofproducing high quality images.

The polyglutarimides of the negative photoresist system include theimidized acrylic polymers described in U.S. Pat. No. 4,246,374 toKopchik, the disclosure of which is incorporated in pertinent part byreference herein. The polyglutarimide must have at least about fivepercent by weight glutarimide units of the following structural formula:##STR1## where R₁, R₂, and R₃ independently represent hydrogen orunsubstituted or substituted alkyl, aryl, aralkyl or alkarylhydrocarbons having from one to twenty carbon atoms or mixtures thereof.Polyglutarimides are formed by reacting an acrylic polymer containingunits derived from esters of acrylic or methacrylic acid, such aspolymethyl methacrylate homopolymer or copolymers of polymethylmethacrylate, with ammonia, primary amines or mixtures thereof.Polyglutarimides can be prepared so that they are soluble in aqueoussolutions when at least about 20 weight percent and preferably 50 weightpercent or more of the R₃ substituent of the glutarimide units arehydrogen. This is accomplished when the acrylic polymer is imidized withammonia or with equal amounts of ammonia and an alkyl amine. It ispreferable to prepare the polyglutarimides by imidizing polymethylmethacrylate with ammonia to obtain the optimum degree of aqueoussolubility. Mixtures of ammonia derived and alkyl amine derivedpolyglutarimides can be prepared and used to adjust the other physicalproperties of the photoresist.

The polyglutarimides may be prepared by a continuous extrusion process,as described in U.S. Pat. No. 4,246,374. The degree of imidization ofthe polyglutarimide can be adjusted by varying the process conditionssuch as residence time, pressures and temperatures. Polyglutarimideswith from about 80 to about 95 percent imidization can be readilyachieved by converting the ester moieties of the acrylic polymer toglutarimide units.

The physical properties of the resulting photoresist film can also beadjusted by varying the molecular weight of the polyglutarimide.Typically, the molecular weight of the polyglutarimide is equal to orapproximates the molecular weight of the precursor acrylic polymer.Therefore, by selecting an acrylic polymer of known molecular weight,the film properties of the negative resist can be optimized for eachadmixture of polyglutarimide and photosensitizer dissolved in selectedsolvent. Typically, the molecular weight of the polyglutarimides usefulin the negative resists of the invention range from about 2,000 to about500,000 weight average molecular weight, and more preferably, from about5,000 to about 200,000 weight average molecular weight.

One of the distinguishing characteristics of polyglutarimides whichmakes them especially useful in photoresist systems is their high degreeof thermal stability. The thermal stability of a polyglutarimideincreases with increasing percent imidization. A 95 percent imidizedpolyglutarimide, derived from ammonia, has a glass transitiontemperature (Tg) of about 250° C. and a Tg midpoint of 231° C. asdetermined by Differential Scanning Calorimetry (DSC). A nearlycompletely imidized polyglutarimide, 95% imidization, derived fromn-methylamine has a Tg of about 180° C. Depending on the processconditions, the ratio of ammonia to alkyl amine, and the type of acrylicpolymer precursors and the extent of imidization, the thermal stabilityof the polyglutarimide, as determined by its glass transitiontemperature or VICAT softening point (ASTM DI 525-70), can range fromabout 130° C. to about 250° C. It is preferable to use polyglutarimideswhich are at least 80 percent imidized with a Tg of at least 140° C.,preferably up to about 180° C., and in certain cases, as for examplewhen reactive ion etching is utilized, even more preferably up to about240° C. The thermal stability of the polyglutarimide is important whenhigh image resolution of less than four micrometers is desired.Thermally stable photoresist films prevent flow of the film when thefilm is exposed to high surface temperatures such as when ionimplantation or reactive ion etching is utilized. Ion doping orimplantation of the silicon wafer surface is used to improve theelectrical conductivity of the silicon wafer. Doping of the silicon isachieved by implanting conductive ions, such as phosphorus or boronions, into the exposed silicon wafer surface. The rate at which suchions can be implanted into the silicon surface is a function of thethermal stability of the photoresist layer. Ion implantation leads tohigh film surface temperatures which can lead to deformation of theimages. If the photoresist film begins to flow during ion implantation,the level of doping and electrical properties of the wafer, as well asimage resolution, will suffer.

In addition, reactive ion etching also requires a highly thermallystable photoresist film. Polyglutarimide resist films are highlyresistant to reactive ion etching and allow the substrate to be rapidlyetched giving increased wafer throughput and lower processing costs.

The polyglutarimide and the conventional, negative-actingphotosensitizer in the resist film react upon exposure of a portion ofthe film to selected radiation. Upon exposure of the resist film to theselected radiation, the solubility of the polyglutarimide polymer in adeveloper decreases to a point that the product can be termed insolublein the developer. The insoluble reaction product is not soluble in thedeveloping solution, such as an aqueous base or a non-aqueous solvent,and development of the unexposed portions in the developer results inthe formation of images on the substrate. The ability of thepolyglutarimide to crosslink with the activated photosensitizers can beenhanced by substitution of the R₃ hydrogen substituents of theglutarimide units with suitable unsaturated compounds (referred toherein as "functionalization"). Suitable unsaturated compounds includealkenyl halides and alkenyl aromatic halides such as allyl, crotyl,butenyl and cinnamyl bromide. This functionalization reaction isconducted by reacting the ammonia derived glutarimide units (R₃substituent is hydrogen) with the unsaturated compound in a solvent,such as dimethylformamide, using a catalyst such as potassium carbonate.The fraction of the R₃ substituents which are substituted by theunsaturated compound may be controlled either by varying the percentageof the hydrogen R₃ substituents in the polyglutarimide starting materialor by adjusting the ratio of unsaturated compound reactant to hydrogenR₃ substituent. If fewer moles of the unsaturated compound are used thanthe moles of hydrogen R₃ substituent then the resulting substitutedpolyglutarimide will still contain some unsubstituted hydrogen R₃substituents.

Partially functionalized polyglutarimides, containing at least about 20weight percent unsubstituted hydrogen R₃ substituents after partialfunctionalization, can be mixed with water soluble negativephotosensitizer compounds, such as those described in U.S. Pat. No.3,917,794 and dissolved in an aqueous base solution to form the negativephotoresist system. This aqueous-formulated negative photoresist systemcan be deposited on a substrate to form an adherent, high quality filmwhich can be exposed and developed using an aqueous base developer. Thissystem completely avoids the need for any organic solvent to eitherformulate the negative resist system or to develop the exposed filmdeposited therefrom. The aqueous base developer does not induce swellingof the exposed film reducing image resolution and the polyglutarimideassures high temperature stability and etch resistance to the resistfilm. These partially functionalized polyglutarimides can alternativelybe dissolved in a suitable organic solvent with a photosensitizer andsuch a resist system can be developed using an organic solventdeveloper.

If the polyglutarimide is completely functionalized with an unsaturatedcompound, leaving less than about 20 weight percent hydrogen R₃substituents, the polyglutarimide is not soluble in water and thereforemust be dissolved in an organic solvent and may be used with an organicsolvent-soluble negative-acting photosensitizer to form a photoresistsystem of the present invention. This negative photoresist systemexhibits rapid crosslinking upon exposure, but requires organic solventdevelopers. The completely functionalized polyglutarimide dissolved inan organic solvent can be used as a negative photoresist system withoutthe addition of a photosensitizer. When this negative resist is exposedto deep UV radiation, the exposed, functionalized polyglutarimidebecomes insoluble and images can be created on the substrate bysubsequent development of the resist.

In the case where the polyglutarimide is not functionalized and containsat least about 20 weight percent hydrogen R₃ substituents, the resist istypically formulated using an organic solvent and organic solventsoluble photosensitizer. The deposited resist film can be developedusing an aqueous base developer.

Therefore, according to the structure of the polyglutarimide, the extentof functionalization, the selection of a compatible negative-actingphotosensitizer and the exposing radiation employed, negative resistscapable of being formulated and developed using aqueous or organicsolutions can be employed.

The negative-acting photosensitizers which are useful with thepolyglutarimides in the negative resists of the invention includeconventional azides and bisazides. When the negative resist isformulated with an organic solvent, the negative-acting photosensitizersare selected based on their compatibility with the polyglutarimide andtheir solubility in the organic solvent which dissolves thepolyglutarimide. The photosensitizer may be sensitive to either near UV,mid UV or deep UV radiation. Near UV as used in this application refersto ultraviolet light having a wavelength ranging from about 310 to about465 nanometers, mid UV refers to ultraviolet light having a wavelengthrange of from about 280 to about 310 nanometers, and deep UV refers toultraviolet light having a wavelength ranging from about 230 to about280 nanometers. Useful negative-acting near UV photosensitizers include2,6-bis(4-azidyl benzylidene)-4-methyl cyclohexanone, and others such asthose described in U.S. Pat. Nos. 4,329,419 and 3,669,669 andPhotoresist Materials and Processes, W. S. DeForest, McGraw-Hill BookCompany, 1975, chapter 2, pages 38-40. Useful negative-acting deep UVphotosensitizers include 3,3'-diaziododiphenyl sulfone and others suchas those described in T. Iwayanagi et al, J. Electrochem. Soc., Vol.127, page 2759 (1980). When the negative resist is formulated with anaqueous base, the negative-acting photosensitizers include water-solublebisazides such as 4,4'-diazido-stilbene-2,2'-disodium sulfonate (nearUV) and others such as those described in U.S. Pat. No. 3,917,794.

Organic solvents useful for forming the negative photoresist system,include N-methyl pyrrolidinone (NMP), N,N-dimethyl acetamide (DMAC),dimethylformamide (DMF), cyclopentanone, cyclohexanone, methyl carbitol,2-methoxyethanol, tetrahydrofuran, tetrahydrofurfuryl alcohol,chlorobenzene, cellosolve acetate, xylene, butylacetate and mixturesthereof.

Typically, the polyglutarimide is dissolved in the solvent, organic oraqueous as the case be, to prepare a 5 to about 30 weight percentsolution. The sensitizer is typically added to the solution atconcentrations of from about 1 to about 50 weight percent, andpreferably from about 1 to about 10 weight percent, based on the amountof the polyglutarimide. Other additives such as adhesion promoters andplasticizers may also be added to the photoresist system.

The negative resist system is capable of being spun cast from thesolution onto an oxide coated, nitride coated or uncoated silicon wafer,or onto aluminum coated substrates, to deposit the resist film. Adhesionpromoting primers such as hexamethyl disilazane (HMDS), beta-3,4-epoxycyclohexyl ethyl trimethoxy silane, and the like can alternatively bespun onto the substrate prior to depositing the resist film. Thethickness of the film deposited can be controlled by adjusting the levelof polyglutarimide and sensitizer solids in the solution and bymodifying the deposition technique such as the speed of spin casting.

Any conventional spin casting method such as those described inIntegrated Circuit Fabrication Technology, D. J. Elliott, McGraw-HillBook Company, 1982, chapter 6, pages 125-144, can be utilized with thephotoresist system of the invention.

Typically, the wafer is placed on a rotating disc, such as a Headway®wafer spinner, and rotated at speeds of from about 2,000 to about 7,000revolutions per minute for from about one-half a minute to about oneminute. The photoresist system is introduced onto the wafer, by either acontinuous or dropwise addition while the wafer is stationary, or whileit is spinning, to deposit the film of uniform thickness on the wafer.The thickness of the deposited film will generally range from about 0.5micrometer to about 3 micrometers. The film is then heated for about 15to about 60 minutes at temperatures of about 60° C. to about 120° C.(referred to as a "soft bake") to reduce the solvent content of thefilm. The film thus deposited is uniform, striation-free and free frompinholes and voids which could lead to reduced quality and yields duringprocessing.

The film is then exposed to radiation through a suitable photomask. Theradiation activates the photosensitizer and causes insolubilization,typically by a crosslinking reaction, of the exposed film to thedeveloper. The unexposed film areas remain soluble in the developingsolution. The film is then developed in any conventional manner such asby immersion to form the images. The imaged wafer is then "postbaked"such as in a forced air oven at about 150° C. to about 180° C. for aboutone hour. If desired, the wafer can be "hard-baked" at temperatures upto about 250° C. for about one half an hour without any noticeable imagedistortion. Following the postbaking and optional hard-baking steps, thewafer can be wet etched or dry etched to remove the oxide from theunexposed areas of the oxidized substrate. It is also possible toutilize the negative resist systems of the invention as thin top layersin multilayer photoresist systems with compatible negative or positiveresist planarizing layers.

The following examples are presented solely to illustrate the inventionand should not be considered to constitute limitations on the scope ofthe invention.

EXAMPLE 1 Complete Functionalization of Polyglutarimide

The starting polyglutarimide polymer (Polymer I) having a molecularweight of 71,000 and a Tg of 199° C. (Differential Scanning Calorimetry)was prepared with 86% imidization, from polymethyl methacrylate andammonia in an extruder, according to the process described in U.S. Pat.No. 4,246,374. The polyglutarimide contained 58 mole % NH (R₃ =H) and 42mole % NCH₃ (R₃ =CH₃) groups. 15.3 grams of Polymer I were dissolved in225 grams of dimethylformamide (DMF) by heating to 70° C. and stirringunder anhydrous conditions. To this solution was added 9 grams ofanhydrous potassium carbonate followed by the dropwise addition of 15grams of allyl bromide. The mixture was stirred and heated at 70° C. for16 hours. Following this, the mixture was cooled to ambient temperatureand poured with stirring into one liter of water acidified with 20 ml.of hydrochloric acid. The white precipitate that formed was filteredusing a Whatman No. 1 filter, washed five times with 300 ml. ofdeionized water, dried in vacuum, and transferred to a 1 liter flask. Tothe flask, 500 ml. of methanol was added and the contents were stirredfor 30 minutes. After similar filtration and drying steps, the productwas weighed and analyzed by NMR which showed the complete substitutionby the N-allyl groups. The product weighed 15 grams and contained 7.34weight % nitrogen. One hundred percent allyl functionalization of thepolyglutarimide was calculated to produce a product containing 7.25weight percent nitrogen.

I also prepared completely functionalized polyglutarimides utilizing theabove procedure with n-crotyl bromide, n-butenyl bromide, and n-cinnamylbromide in place of the allyl bromide.

EXAMPLE 2 Use of Substituted Polyglutarimide Negative Resist

The completely n-allyl substituted polyglutarimide prepared in example 1was then used in formulating a negative photoresist. One gram of then-allyl substituted polyglutarimide was dissolved in 5 grams ofdimethylformamide. To this solution was added 0.1 grams of2,6-bis(4-azidylbenzylidene)-4-methylcyclohexanone sensitizer to formthe resist system. The solution was then filtered through a 0.45micrometer Millipore filter. Two ml. of the resist system was thenpipetted onto a three inch diameter silicon water, having a onemicrometer thick silicon oxide layer, and spun, using a Headway® Waferspinner at 3000 rpm for 60 seconds, to deposit the resist film on theoxide layer. The film was then soft baked at 90° C. for 30 minutes. Theresulting resist film had a thickness of 1.45 micrometers as measured bya TenCor Alpha Step Profilometer. The film was clear and striation-free.

A photomask was placed in contact with the photoresist film using an HTGcontact printer. The mask had lines and spaces ranging from 0.75micrometers to 5 micrometers in width. Nitrogen gas was added for 5seconds and a contact vacuum was established between the mask and thewafer. The film was then exposed through the mask to near UV radiationwith an intensity of 20 milliwatts (MW) per cm² at 365 nanometers for 3seconds.

The exposed wafer was then immersed in a DMF developer bath for 30seconds, with hand agitation, removed from the developer bath andair-dried.

The resulting images were then examined using an optical microscope. Theimage resolution was 2 micrometers and no effects due to swelling wereobserved. The post-development film thickness was 1.17 micrometers.

Similarly, other negative resists containing completely functionalizedpolyglutarimides, prepared according to example 1, were formulated withthe same bis-azide sensitizer and evaluated as negative resists underthe same exposing radiation conditions as above. The results are shownin Table 1.

                                      TABLE 1                                     __________________________________________________________________________                               Film                                                                          Thickness                                          Unsaturated                Initial                                                                             Final Minimum                                Substituent                                                                          Depositing                                                                            Developing  Thickness                                                                           Thickness                                                                           Resolution                             R.sub.3                                                                              Solvent Solvent     Micrometers Micrometers                            __________________________________________________________________________    n-crotyl                                                                             cyclopentanone                                                                        cyclopentanone (70° C.)                                                            0.6   0.5   2                                      n-butenyl                                                                            cyclopentanone                                                                        cyclopentanone (70° C.)                                                            0.6   0.5   2                                      n-cinnamyl                                                                           cyclopentanone                                                                        cyclopentanone (70° C.)                                                            0.6   0.5   2                                      __________________________________________________________________________

EXAMPLE 3 Deep UV Completely Substituted Polyglutarimide Negative Resist(with sensitizer)

The n-allyl substituted polyglutarimide of example 1 was also used toformulate a deep UV sensitive negative resist system. One gram of thepolyglutarimide was dissolved in 5 grams of N-methyl pyrrolidinone. Tothe solution 0.1 grams of 3,3'-diazidodiphenyl sulfone was added. Theresist system was filtered through a 0.45 micrometer Millipore filterand 2 ml. of the resist was deposited onto a one micrometer thick oxidecoated 3 inch diameter silicon wafer and spun cast at 3000 rpm for 60seconds. Following a 30 minutes soft bake at 90° C. the thickness of thefilm was measured to be 1.1 micrometers. The film was clear andstriation free. The resist film was then exposed to deep UV radiationwith an intensity of 18 MW/cm² at 254 nanometers for 2.5 seconds throughthe contact vacuum mask as described in example 2. The film wasdeveloped in a DMF bath for 30 seconds and resulted in image resolutionof 2 micrometers with a 0.6 micrometer thick film after development.

EXAMPLE 4 Non-Functionalized-Solvent Formulated/Aqueous DevelopedNegative Resist

A starting polyglutarimide polymer (Polymer II) having a molecularweight of 33,000 and a Tg of 207° C. (DSC) was prepared with 86%imidization, from polymethacrylic acid and an ammonia precursor in anextruder, according to the process described in U.S. Pat. No. 4,246,374.The polyglutarimide contained 100% ammonia imide (R₃ =H) groups. Onegram of Polymer II was dissolved in 4 grams of dimethylformamide. Tothis solution was added 0.1 gram of 2,6-bis(4-azidylbenzlidene)-4-methylcyclohexanone sensitizer. The solution was filtered through a 0.45micrometer Millipore filter.

The resist system was spun cast onto a one micrometer thick siliconwafer oxide coated 3 inch diameter silicon wafter by spinning at 3000rpm for 60 seconds. After a 30 minute softbake at 90° C., the filmthickness was measured to be 2.4 micrometers and appeared clear andstriation-free.

The photomask used in the preceding examples was placed in contactvacuum with the film and the film was exposed to near UV radiation withan intensity of 20 MW/cm² at 365 nanometers for 4 seconds.

The exposed wafer was immersed in an aqueous developer (Shipley MF 312,an aqueous base containing tetramethyl ammonium hydroxide, diluted sixtimes with deionized water) for 40 seconds with gentle agitation,removed from the developer and dried. The image resolution achieved was2 micrometers with a film thickness of 0.7 micrometers.

EXAMPLE 5 Preparation of Partially Functionalized Polyglutarimide

15.3 grams of Polymer II of example 4 was dissolved in 225 grams of DMFby heating to 70° C. and stirring under anhydrous conditions for onehour. Five grams of potassium carbonate was added to the solutionfollowed by dropwise addition of 6 grams of allyl bromide. The mixturewas stirred and heated at 70° C. for 16 hours. Following this partialfunctionalization, the polyglutarimide solution was cooled to ambienttemperature, and poured with stirring into one liter of water acidifiedwith hydrochloric acid. The white precipitate that formed was filteredthrough a Whatman No. 1 filter, washed 5 times with 300 ml. of deionizedwater, air-dried and redissolved in DMF and reprecipitated from water.The precipitate was then stirred with 500 ml. of methanol for 30minutes, filtered through a Whatman No. 1 filter and dried in vacuum.The product weighed 15.6 grams and was 50% allyl and 50% hydrogenfunctionalized as determined by NMR Spectrum.

EXAMPLE 6 Use of Partially Functionalized Polyglutarimide NegativeResist

The 50% n-allyl functionalized polyglutarimide of example 5 was used toprepare a negative resist. One gram of the partially functionalizedpolyglutarimide was dissolved in 5 grams of DMF. 0.08 grams of4,4'-diazido-stilbene-2,2'-disodium sulfonate was added to the solution,dissolved and filtered through a 0.45 micrometer millipore filter.

A three-inch diameter silicon wafter having one micrometer thick siliconoxide coating was primed with 1 ml. of hexamethyl disilazane by spincasting the primer at 3000 rpm for 30 seconds onto the oxide surface.The resist solution was then spun on top of the primer by spinning at3000 rpm for 60 seconds. Following a 30 minute soft bake at 90° C., thefilm had a thickness of 1.25 micrometers and was clear and striationfree.

The photomask was placed in contact vacuum with the film as described inthe prior examples and the film was exposed to near UV radiation withintensity 20 MW/cm² at 365 nanometers for 20 seconds. The exposed waferwas then immersed in an aqueous base developer (Shipley 351, an aqueoussodium hydroxide solution, diluted with equal volume of deionized water)for 30 seconds with gentle agitation and was dried. Image resolutionsdown to 2 micrometers were obtained with a 0.5 micrometer film thicknessafter development.

EXAMPLE 7 Aqueous Base Polyglutarimide Negative Resist

The polyglutarimide of example 5 (R₃ =50% allyl and 50% hydrogen) wasused to formulate an aqueous base, negative photoresist system. One gramof the partially functionalized polyglutarimide was dissolved in 10grams of Shipley MF 312 tetramethyl ammonium hydroxide. 0.1 grams of awater soluble, 4,4'-diazidostilbene-2,2'-disodium sulfonate sensitizerdissolved in 2 grams of deionized water with gentle warming to 35° C.The solution was then cooled to 20° C. and it was then added to thepolyglutarimide solution, mixed thoroughly, filtered through a 0.45micrometer Millipore filter and spun coated on a three-inch diametersilicon wafer containing 1 micrometer thick silicon oxide layer.Spinning was conducted at 2000 rpm for 60 seconds. After a 30 minutesoft bake of the wafer at 105° C., the resist film thickness was 0.75micrometers. The film was then exposed through the contact vacuumphotomask to near UV radiation with an intensity of 20 MW/cm² at 365nanometers for 60 seconds. The wafer was then immersed in an aqueousbase developer (Shipley 351 diluted with three times its volume ofdeionized water) gently agitated for 30 seconds and dried. Imageresolutions down to 4 micrometers and a film thickness of 0.2micrometers was obtained.

EXAMPLE 8 Deep UV Completely Substituted Polyglutarimide Negative Resist(Without Sensitizer)

The starting polymer, Polymer II (in Example 4), was completelysubstituted with allyl groups (R₃ =allyl) as in Example 1 using allylbromide. One gram of the allyl substituted imide was dissolved in 5grams of dimethylformamide and filtered through a 0.45 micrometerMillipore filter. Two milliliters of the resist system was then pipettedonto a two inch silicon wafer with a one micrometer thick oxide and spunon a Headway Spinner for 60 seconds at 2000 rpm. The film was thensoftbaked at 90° C. for 30 minutes. The resulting resist film had athickness of 0.7 micrometer and was clear and striation-free.

The photomask was placed in contact vacuum with the film as described inthe previous examples and the film was exposed to deep UV radiation withan intensity of 8 MW/cm² at 254 nanometers for 20 minutes. The exposedwafer was immersed in dimethylformamide with gentle agitation for 30seconds and air-dried. Image resolutions down to 1 micrometer wereobtained in a 0.7 micrometer thick film after development.

The film was post-baked in an oven at 250° C. for 1 hour. All the imageswere retained in good condition with the film thickness down to 0.65micrometer. The wafer was subjected to Reactive Ion Etching using CHF₃plasma. The power density was 1100 watts, the cathode/wafer potentialdifference was 600 V. While the oxide loss was 0.34 micrometer, theresist loss was only 0.07 micrometer, giving an oxide-to-resist etchratio of 4.9.

What is claimed is:
 1. A process forming an image on a surfacecomprising depositing a negative acting photoresist film on saidsurface, said film comprising a polyglutarimide polymer and anegative-acting photosensitizer dissolved in a solvent wherein saidpolyglutarimide polymer comprises at least about 5 wt% glutarimide unitsof the formula: ##STR2## where R₁, R₂, and R₃ independently arehydrogen, unsubstituted and substituted alkyl, aryl, aralkyl or alkarylhydrocarbons having from one to twenty carbon atoms or mixtures thereof,where at least about 20 mole percent of the R₃ substituents are hydrogenand where said negative-acting photosensitizer is selected from thegroup consisting of photosensitive azides and bisazides and is presentin said photoresist at a sufficient quantity to enable the photoresistto become insoluble in an aqueous developer upon exposure of thephotoresist to actinic radiation,softbaking said film, exposing aportion of said film to a source of actinic radiation that decreases thedissolution rate of said polyglutarimide in an aqueous developer, andremoving the unexposed portion of said film with said aqueous developerto form said image.
 2. The process of claim 1 wherein said exposingradiation is selected from the group consisting of near, mid and deepultraviolet light.
 3. A process for forming an image on a surfacecomprising depositing a negative acting photoresist film on saidsurface, said film comprising a polyglutarimide polymer dissolved in asolvent wherein said polyglutarimide polymer comprises at least about 5wt% glutarimide units of the structural formula: ##STR3## where R₁, R₂,and R₃, prior to functionalization, are hydrogen, unsubstituted andsubstituted alkyl, aryl, aralkyl or alkaryl hydrocarbons having from oneto twenty carbon atoms or mixtures thereof, and where all the R₃hydrogen substitutents are functionalized by reacting said R₃ hydrogensubstitutents with an unsaturated compound selected from the groupconsisting of alkenyl halides and alkenyl aromatic halides,soft bakingsaid film, exposing a portion of said film to deep ultra violet lightand removing the unexposed portion of said film with an organicdeveloper.
 4. The process of claim 3 wherein said alkenyl halide isselected from the group consisting of allyl bromide, crotyl bromide andbutenyl bromide.
 5. The process of claim 3 wherein said alkenyl aromatichalide is cinnamyl bromide.
 6. The process of claim 3 where the filmfurther comprises an effective amount of an organic solvent-soluble,negative acting photosensitizer.